Human Rights Watch said Tuesday that strong evidence shows that Syrian regime forces launched chemical attacks on Idlib province in northern Syria.

According to a written statement by the international organization, the Assad regime used toxic chemicals in several barrel bomb attacks on Idlib between March 16 and 31.

The assaults, which violated the Chemical Weapons Convention and a United Nations Security Council resolution, affected at least 206 civilians, including 20 civil defense workers, HRW said.

The attacks also killed six civilians, including three children, the organization added.

“Syrian authorities appear once again to have shown complete disregard for human suffering by violating the global prohibition against chemical warfare,” Nadim Houry, HRW deputy Middle East and North Africa director, said. “The UN Security Council and countries that are members of the Chemical Weapons Convention need to respond strongly.”

Human Rights Watch said it documented evidence of three chemical attacks through photos, videos and eyewitnesses, who described smelling chlorine.

The Syrian opposition has repeatedly accused the Assad regime of using chemical and toxic weapons against civilians since August 2013, when a single attack reportedly killed more than 1,400 civilians.

Anadolu Agency